Transition metals are of increasing importance in a variety of electronic and electrochemical applications. This is because transition metals are excellent electrical conductors, are generally unreactive and resist oxidation. In addition, late transition metals form stable interfaces with high dielectric constant (high-k) materials and form good electrical contacts with other metals used for interconnection. Thus, the late transition metals have suitable properties for a variety of uses in the formation of an integrated circuit (IC). They are particularly suitable for use as electrodes in high-k capacitors and ferroelectric capacitors, and in metallization stacks and barriers between dielectric material and silicon substrates in semiconductor devices.
The increasing use of late transition metals in electronic and electrochemical applications requires a reliable manner of etching such metals. However, late transition metals are difficult to uniformly and selectively etch. Late transition metals, such as platinum, rhodium, iridium, palladium, copper, cobalt, iron, nickel, silver, osmium, gold and ruthenium, are conventionally wet etched using aqua regia or ion milling. Halogen-containing gases, such as chlorine gas or hydrogen bromide, and oxygen have also been used to plasma etch platinum. Since the late transition metals are relatively unreactive, highly reactive etchants are typically used. However, if during fabrication, the IC includes other exposed materials, such as main group metals, early transition metals, hardmask materials or photoresist materials, these highly reactive etchants remove the other exposed materials at a faster rate than the late transition metal or damage the other exposed materials. Alternatively, high temperature etching is used to increase the etch rate of the unreactive late transition metal. However, other exposed materials, such as hardmask or photoresist materials, are not typically compatible with high temperature, corrosive etches.
U.S. Pat. No. 6,846,424 discloses a process for plasma etching noble metal-based material structures. The noble metal-based material is etched using a halogenated organic compound and a gas that provides an oxidizing ambient environment. The gas is included to prevent the deposit of polymeric by-products on a surface of an etch chamber.
Since late transition metals are unreactive and difficult to selectively and uniformly etch, improved etchants and methods of removing the late transition metals are desired.